Non Posi On HP motor

[Jack A.]

Hi Guys,

I think I know the answer on this but I need to be sure. I am looking at a numbers matching 61 270 HP solid lifter car. All the numbers are correct on motor an transmission etc. The question in on the differential. It has a Non Posi unit. The numbers and are correct for a late 61 but I don't remember seeing a Hi Performance engine without a Posi. I already have a Top Flight 61 Fuelie so I know a little about them.I would think as an option it is OK, but seems odd. Thoughts??

Thanks,

Jack 35730

[David R.]

Re: Non Posi On HP motor

For what it's worth, my February 1962 300hp is an original non-posi car - pretty rare for the year. Out of total 1962 production of 14,531 only 299 were non-posi from the factory.

[Joe L.]

Re: Non Posi On HP motor

Hi Guys,

I think I know the answer on this but I need to be sure. I am looking at a numbers matching 61 270 HP solid lifter car. All the numbers are correct on motor an transmission etc. The question in on the differential. It has a Non Posi unit. The numbers and are correct for a late 61 but I don't remember seeing a Hi Performance engine without a Posi. I already have a Top Flight 61 Fuelie so I know a little about them.I would think as an option it is OK, but seems odd. Thoughts??

Thanks,

Jack 35730

Jack------


Is it unusual? Yes. Is it possible? Also yes.

Positraction was not a required option for any engine option for 1961.

[Loren L.]

Re: Non Posi On HP motor

Ordered by a dealership dummy who didn't know what Positraction was - keep the price down! It would sell anyway
. The buyer of a 300 HP did not intend to be "king of the road".

[Tom D.]

Re: Non Posi On HP motor

Seems like this was true in the case of a silver '61 formerly owned by Rick Boyd of Mich. I have photos somewhere...

[David B.]

Re: Non Posi On HP motor

For anyone willing to listen, the positraction production numbers for the '62 Corvette has been INCORRECT for years.
GM Production breakdown for 1962 option RPO - 675 is:
3.70 -- 1,313
4.56 -- 897
3.36 --3,238
" -- 3,787
3.55 -- 348
3.08 -- 99
" -- 995
" -- 116
___________
10,793 TOTAL

[Jack A.]

Re: Non Posi On HP motor

Thank you gentlemen. Really appreciate you taking the time to respond. You have helped me with so much over the many years.
Warmest Regards,
Jack Alexander 35730

[David R.]

Re: Non Posi On HP motor

For anyone willing to listen, the positraction production numbers for the '62 Corvette has been INCORRECT for years.
GM Production breakdown for 1962 option RPO - 675 is:
3.70 -- 1,313
4.56 -- 897
3.36 --3,238
" -- 3,787
3.55 -- 348
3.08 -- 99
" -- 995
" -- 116
___________
10,793 TOTAL

I appreciate your attempt to correct the "incorrect" figure of 299 for non-posi 1962 cars, which (as we all know) appears in several places. How do you arrive at your figures, where are they from, and what do they mean? The way you present them appears to list more than one production total for the same rear end ratio. Are they broken down by transmission type (3-speed, 4-speed, Powerglide)? By engine selection (250hp, 300hp, 340hp, 360hp)? Just trying to understand.

[Loren L.]

Re: Non Posi On HP motor

David, I note that the NCRS Pocket Spec Guide asterisks '61 Posi as available with only manual transmission but the listing for '62 Posi does NOT - are the 1532 PG Vettes in '62 still not
available with Posi?

[Ed H.]

Re: Non Posi On HP motor

Jake, the stamp pad on the front of the block will have numbers and letters which indicate engine Hp and trans type. That info will tell a lot. You stated the vehicle was a 270 Hp. that would mean it has a casting number, last 3, of 519 for an early car and 935 for a very late car. A non-posi rear end would be stamped AH and a posi would be AN, those two would be 3.70 ratio. If you have a 1953 to 1967 NCRS Specific Guide the rear end ratios are listed on page 72 and 73, there are 14 different listings from 3.36 standard 3-Spd to the 4.56 big brake cars. It would be interesting to know what the stamping on the left side of the third member, and the casting number on the right side. Look for a plate attached on the upper right side for a tag, held on by a nut, located at the 2 or 3 o'clock position. The configuration of this small plate should tell you the ration of the third member. Hope this helps.

[David B.]

Re: Non Posi On HP motor

Production #s listed obtained from GM Tech Center decades ago. Probably the same source as you referenced. Note your sources list totals only and not breakdowns. For some reason RPO-675 for the '62 Corvette was never listed correctly by these sources. RE: Your question, the breakdown quoted was a little more detailed (not by much) the repeat of some ratios was copied as recorded and could refer to Engine or Transmission type, I am not sure which since letter designations which accompanied each did not explain their meaning. The '61 Corvette RPO-675 option lists 382 Corvettes with the 3.36 ratio and as mentioned I cannot decipher if powerglide or not. For what its worth, the Spec Guide mentioned previously has been out of date for years especially 56-57 until updated would recommend saving your money.
As you will note, my computer skill in listing the breakdown needs major improvement!

[Tom P.]

Re: Non Posi On HP motor

For those folks who have a matching number car WITHOUT posi, but would really like to have a posi, then a posi can be (fairly easily) added.
I put this article together several years ago about adding a posi to a NON-posi 56-62 case for Corvettes (55-64 for pass cars).

[Daniel R.]

Re: Non Posi On HP motor

I have a 62 with a 308 posi. Must be pretty rare !

[Tom P.]

Re: Non Posi On HP motor

I have no idea how common (or uncommon) a 3.08 posi was in 62 Corvettes. But since this same style rear continued to be used up through 64 in pass cars, the 3.08 was moderately common in 62-64 pass cars, and quite a few were posi.
With today's gas prices being so high, hiway gears are more to my liking than tire burning 4.11 or 4.56 gears.
I have three cars that use this type rearend, and all 3 have 3.08 posi rears----------------plus a couple of spares ready to go under the workbench.